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Understanding Calcium, UVB and Vitamin D3 in Lizards.

Understanding Calcium, UVB, and Vitamin D3 in Lizards
Why?:
This particular topic has a tendency of sounding Greek or Chinese to many beginner reptile owners or even experienced ones who get a migraine looking at technical jargon. As a result this topic has a tendency of leading to misinformation and it's important to prevent this. Unlike most pets out there reptile owners are not granted the luxury of a forgiving husbandry. The adaptability of cats and dogs to their environment over reptiles afford pet owners the choice to engage in a more thorough understanding of their animal. Choosing not too usually won't severely compromising the longevity of its health. With reptiles this is not the case. Their sensitivity to light and heat place a greater responsibility upon their owners to pay attention to details when providing an adequate home.

[Disclaimer]I do not doubt that someone with a science background could critique this article and provide additional clarity, but this article is not intended for scholarly sourcing, but merely as a basic guide to help most reptile owners avoid common errors in their husbandry.
Breakdown:
As an attempt to aid in the flow of this article, a glossary will be provided at the bottom. Words in Red can be found at the bottom of the end of the article with proper definitions.

What is the relationship between UVB, Calcium, and Vitamin D3?:
UVB rays aid in the photosynthesis of vitamin D3, which is then used to properly metabolize calcium. In short the process can be remembered as follows:UVB->Vitamin D3->Calcium = Healthy Bones

Who applies:
Pretty much any Diurnal reptile applies to the importance of UVB radiation; however its additional importance to various Nocturnal reptiles should not be underestimated. Just because a reptile is active at night and not exposed to long durations of UVB does not trivialize its overall importance. Many nocturnal reptiles are carnivorous, and therefore obtain vitamin D3 through the digested liver of their prey, but this process does not always guarantee sufficient vitamin D3 levels. Some nocturnal reptiles will naturally compensate for this by sleeping in areas exposed to daylight (even for a short period) attaining the proper UV radiation it needs. Other reptiles will actively bask in the early or late hours of the day while reserving night hours for foraging and hunting. If you own a nocturnal reptile it would be to your own benefit and your reptile's to find out if it is one of these nocturnal species. At the end of he day a couple minutes of your time could add a couple years onto your reptile's life.

What is UVB radiation?
To understand what UVB rays are, we should first look at the electromagnetic spectrum. To avoid the risk of engaging in any scientific jargon, and for the sake of what's important to reptiles, it will suffice to define the electromagnetic spectrum as the full range of energy emitted by the sun.<br>

This is usually where people will get frustrated with the language and give up. In reality there is no reason to get discouraged, because most of this information can be discarded for the sake of what's important to this particular article. So let's gut the none essentials from this picture.

As the diagram indicates frequency and wavelength have a negative correlation; however these measurements are not pertinent to our goal, so they can be removed.

Y-rays (Gamma), X-rays, microwaves, radio waves, and long radio waves are not pertinent to our discussion either so they can be eliminated as well.
This is our final image, much more simplified. In retrospect to the discussion of Vitamin D3, the visible spectrum and Infrared(IR) could be eliminated too, but they do have importance to reptiles so it's better to explain them.

UV rays: these are the UVB and UVA rays emitted from the sun. It also contains the highly dangerous UVC rays, but thankfully they are blocked by the Earth's ozone layer. UVA is not important for vitamin D3 synthesis, but most commercial bulbs that provide UVB will provide UVA as well, not to mention UVA radiation improves the overall physiological well-being of your reptile: ie a happy lizard equals a fun lizard to watch.Visible Spectrum: these are the rays that animate visual color to all living things. In retrospect it makes up such a tiny portion of the suns energy, but a full visible spectrum can be vital to seasonal and mating behaviors.
*On the commercial market, most daylight bulbs will combine UV rays and visible light, which will be covered more thoroughly later.Infrared: these rays are what produce heat.

What is UVB radiation? Con't:
Now that the electromagnetic spectrum has been explained and simplified we can focus on what's most important to us in this article, UVB rays. In the wild reptiles suffice their UVB requirements through natural sunlight. To give a general idea of how affective the sun is; 4 hours of natural sunlight can match the UVB exposure of an entire week under most artificial bulb sold in stores. So what does this mean?The technical explanation:
"UVB reacts with the precursor of vitamin D, 7-dehydrocholestrol, in the skin to produce provitamin D3. Depending on heat and the aid of mechanism in the skin, provitamin D3 is coverted into vitamin D3 itself. The liver and kidneys transform vitamin D3 into its active form, a hormone (1,25, hydroxy-vitamin D) that regulates calcium metabolism."Reptile Lighting Guide, Exo Terra, Hagen Inc, Montreal, Canada: 2011, pg 10.

The simple explanation:
UVB rays are absorbed into the skin of your reptile which aids in the overall production of Vitamin D3. This particular vitamin is essential for metabolizing calcium, which is in turn essential for your reptiles healthy bones. Just try to remember...UVB->Vitamin D3->Calcium = Healthy Bones

Are UVB rays the only natural source of Vitamin D3?:
No, Vitamin D3, as suggested above, can also be obtained through the digested livers of its prey. However, as stated above, this is not always an adequate source for D3, therefore UVB is still essential to carnivorous reptiles.

Can only Vitamin D3 metabolize Calcium?:
No, Vitamin D2 can also metabolize calcium, but it is far less affective. Vitamin D2 is found in plants, and the only natural alternative for metabolizing calcium in reptiles other than Vitamin D3. As a result UVB rays are even more essential to vegetarian repiles.

So what can go wrong?:
As the process indicates, a lack of UVB will result in a lack of Vitamin D3, which in turn will result in a lack of metabolized calcium. The final result is a reptile with very weak bone density referred to a metabolic bone disease. Additional symptoms are/and not limited too: lethargic behavior, tremors, fatigue, and swelling. Secondary problems can occur like broken bones or choking from weakened jawbones used to swallow.

Females Beware:
Many female reptiles will deposit eggs even without the presence of a male counterpart. These eggs are infertile, but the calcium depletion used to produce the eggs is still the same. Therefore female reptiles need even additional calcium during these periods, making the need for Vitamin D3 even more essential to their overall health.

Why not Crank the UVB?
There are probably several reasons that go beyond my comprehension but I will try my best to explain. The most obvious explanation would be radiation poisoning. Mother nature is more experienced at regulating UV rays and protecting us from its dangerous effects than we are.

(1)Ozone Layer: helps filter dangerous UV levels down to acceptable levels.
(2)Longitude/Latitude/Altitude/Earth's-rotation all contribute in a range of continuously fluctuating UV levels. UV gradually
(3)The dense canopy of foliage filters UV exposure in tropical habitats.
*at the end of the day; intensity cannot substitute fluctuation. Just because 4 hours of natural sunlight can equal an entire week of artificial UVB light, does not mean cranking the UV rays will improve its effectiveness. There are simply too many filtration factors that are too difficult to emulate in an artificial habitat.

Why not load up on Vitamin D3?:
Completely regulating vitamin D3 by supplements is plausible and would eliminate UVB rays from the equation, but (to my knowledge) it's a far more demanding responsibility than simply having UVB lighting. UVB deficiencies can lead to MBD, but it is not the inherent cause. The true cause of MBD is a lack of calcium, so in truth, anything that can lead to this should be treated with equal caution. Excessive levels of vitamin D3 can cause kidney damage which will in turn impede calcium levels the same UVB deficiencies would. When strictly sourcing vitamin D3 from supplements the owner must be careful not to overdose D3 as well as under-dose.

Achieving a Balanced Light Cycle:
It's important to understand the output of your bulbs. Different brands appear to prefer different setup models.

Zoo Med: Their compact fluorescent bulbs are said to provide both UV rays and a full visible light spectrum. They can be purchased in both Reptisun 5.0 (tropical) or Reptisun 10.0 (desert) models.

Exo Terra: Their fluorescent bulbs address UV and visible light separately. Repti Glo 2.0 does provide a full range of visible light, but it lacks in adequate levels of UV. This has lead to false beliefs that Exo Terra bulbs do no help against MDB. When dealing with Exo Terra artificial light products it's important to remember their bulbs have a negative correlation between UV and visible light. The strong one is the weaker the other. To get the full lighting effect needed it's best to house this brand of bulbs in pairs. Repti Glo 5.0 (tropical) and Repti Glo 10.0 (desert) provide adequate UV levels for their respective reptiles, but they lack in a full range of visible light. Housing a Repti Glo 2.0 with either a Repti Glo 5.0 or 10.0 will establish a complete lighting setup.

Zilla: They do not sell Zilla bulbs in my area, and maybe for good reason. After a quick look on their website to research the specs of their bulbs, they appear to fall short of proper UV levels.
Glossary:

Diurnal: active in the day time.Electromagnetic Spectrum: the full range of electromagnetic radiation.Husbandry: the full care, cultivation and breeding of an animal.Metabolic Bone Disease: weakened dones due to a lack of metabolized calcium in the diet.Negative Correlation: as one increases the opposite decreases.Nocturnal: active in the night time.Physiological well-being: the way in which a living organism naturally functions.